Apparatus for reducing vaporizable refractory metal compounds



Feb. 19, 1963 M. P. HNILICKA, JR 3,078,082

APPARATUS FOR REDUCING VAPORIZABLE REFRACTORY METAL COMPOUNDS 2 Sheets-Sheet 1 Filed May 6, 1957 INVENTOR. A4110 h wffcka p- BY ATTORNEY 1963, M. P. HNILICKA, JR 3,078,082

APPARATUS FOR REDUCING VAPORIZABLE REFRACTORY METAL COMPOUNDS Filed May 6, 1957 2 Sheets-Sheet 2 Condenser 72 Furnace BY M W. M77141 ATTORNEY Vacuum Sysl'em and Scrubber Fatented Feb. 1%, 1%63 The present invention relates to an improved apparatus for producing metals such as zirconium and the like wherein a normally solid metal halide is reduced by a metallic reducing agent such as magnesium.

A principal object of the present invention is to provide an improved apparatus of the above type which is simple to operate and assures the production of product metal of maximum purity.

Another obiect of the invention is to providean im-' proved apparatus having a high capacity in the tonnage range per batch.

Still another object of the invention is to provide an apparatus of the above type containing safety provisions for maintaining the reaction under control at all times.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the process involving the several steps and the relation and the order of one or more of such steps with respect to each of the others and the apparatus possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings wherein:

FIG. 1 is a diagrammatic, schematic illustration of one part of a preferred embodiment of the invention; and

- FIG. 2 is a diagrammatic, schematic illustration of an-.

other portion of the preferred embodiment of the inven tion.

The present invention will be primarily described in connection with its utility for the production of zirconium metal, particularly by the reduction of zirconium tetra chloride by means of molten magnesium. While the do scription of the invention is initially limited to this preferred application, it is to be understood that the scope of the invention is not so limited.

In the production of zirconium by the reduction of zirconium tetrachloride vapors with molten magnesium, it is extremely important, particularly when the zirconium is to be utilized in atomic energy reactors, that the zirconium have maximum purity. This ecessitates that the reaction temperature be maintained below the temperature at which the forming zirconium will react or alloy with the reaction vessel. Since the reaction between zirconium tetrachloride and magnesium is violently exothermic, considerable difiiculty has een experienced in the past in maintaining proper temperature control. Additionally, it is extremely important that the product metal be completely free of oxides, nitrides and the like since even minute quantities of these materials drastically affect the utility of the final zirconium. These problems are particularly acute when it is considered that zirconium tetrachloride is highly hygroscopic and quite reactive with many materials of construction.

In the present invention the reduction reaction is preferably accomplished in a long, horizontal metallic retort which is posi ioned in a furnace having several separately controlled temperature zones. One end of the retort .is

preferably designed to serve as a reduction zone and the other end of the retort preferably serves as a tetrachloride volatilization zone. A tub containing magnesium and serving as a reaction vessel is positioned in the reduction zone, and several containers or" the solid zirconium tetrachloride are positioned in the halide volatilization zone.

The two zones are preferably maintained at a pressure slightly in excess of atmospheric and are substantially completely thermally isolated from each other and only a small passage is provided near the top of the retort to permit passage of vapors from the volatilization zone to the reduction zone. Since the vapors preferably pass up wardly through a micrometallic filter and then continue at low velocity laterally from the volatilization chamber into the reduction zone, the possibility of entraining finely powdered non-volatile solids in the vapor stream and carrying them into the reduction zone is substantially eliminated.

The walls of the volatilization zone are preferably maintained at a temperature on the order of 10% C. above the sublimation temperature (331 C.) of the zirconium tetrachloride, and the reduction zone is preferably main tained at a much higher temperature (eg 850 C.), which favors the reduction reaction. The volatilization zone preferably includes a condenser by means of which the partial pressure of zirconium tetrachloride vapors in the volatilization zone may be controlled by condensation of these vapors on the condenser. This is achieved in a preferred embodiment by sucking cold air through the coils of the condenser. This cold air is preferably at a subatmospheric pressure so that any condenser leak results in zirconium tetrachloride flowing outwardly from the volatilization zone rather than air flowing inwardly from the condenser. A similar vent condenser is provided adjacent the reaction zone in the reactor vent line. This latter condenser is prefer-ably of the shell and tube type and is positioned in a separate furnace so that the shell is constantly maintained above the condensation temperature of zirconium tetrachloride. The surfaces of the tubes, how ever, may be maintained below the zirconium tetrachloride condensation temperature by sucking cold air through the tubes. When it is desired to revaporize the zirconium tetrachloride, the hot furnace gases may be sucked through the tubes in place of the cold air.

Referring now to FIGURES l and 2, there is shown a diagrammatic, schematic representation of one preferred embodiment of the invention. The apparatus includes the generally horizontal furnace schematically indicated at ii) as having two sections 152, and 14-. These two sec tions separated by a wall 16, are heated by a plurality of separately controllable heatirn elements (indicated schematically at 13) and are cooled, when desired, by blowers i9. Positioned within the furnace is an elongated horizontal retort Zii, defining therewithin two thermally isolated chambers 22 and 2 3-, chamber 22 constituting the reduction zone and chamber 24 constituting the halide volatilizatz'on zone. Retort Ztl is preferably supported on roller bearings 23 and on fixed bearing 25. A large metallic tub 26 containing magnesium 28 constitutes the actual reduction reactor. Containers 352, each having a charge of solid zirconium tetrachloride, hold a charge of zirconium tetrachloride 32 in the volatiliz tion chamber Each container lid is preferably provided with a micrometallic filter 33 on the top thereof to prevent escape of fine powders from container 3d. This filter 3.3 is preferably arranged to fit loosely on the top of the container so that any undue increase of pressure within the chamber can be released by the lifting of the filter.

Tub 2s and containers 3b are preferably supported on legs 34 which keep them spaced from a hearth 36 and thus permit loading of tub 26 and containers 3% onto the hearth with a mechanism such as a fork truck. A bafile arr/span 33, having a hermetically sealed outer metallic shell 37 and filled with insulating material 39, serves to thermally isolate zones 22 and 24. A portion of the baffle 38 is cut away at the top to provide a passage as through which the zirconium tetrachloride vapors can pass into a distributor 42 for guiding these vapors onto the surface of the molten magnesium 23. A controlled pressure of argon or other inert gas is preferably introduced through pipes 43 to maintain the interior of retort 2d at a slight positive pressure.

The end of the horizontal retort 2i adjacent the volatilization chamber 24 is closed by a removable plug generally indicated at 44, this plug comprising a hermetically sealed metallic outer shell 46 and an inner insulating mass 43. The plug preferably carriesa condenser coil 50 on its inner end, this condenser being connected by a flexible hose 52, extending through an outer door 54 to a vacuum pump 56. The other end of the coil can be connected directly, by means of a flexible hose 58 through a valve 57, to the atmosphere to permit pump 56 to suck cold air through the condensercoil 50 when valve 57 is opened. Ordinarily pump 56 maintains the interior of condenser 50 under a vacuum. Plug 44 also preferably includes lifting books 60' for handling by means of a fork lift truck or the like. The hollow plug 4-4 is preferably also provided with a vent pipe 62 extending to the interior thereof to permit the pressure in the interior of this plug to be maintained at the same pressure as that existing within the retort 24). Accordingly, pipe 62 can be connected to a positive pressure of argon or to a vacuum pumping system by means of suitable valves. A similar pipe 64 is provided for equalizing the pressure inside of the shell of the insulating barrier 38, this pipe being connected (in a manner not shown) to a similar source of vacuum or inert gas.

Theend of the retort 26 adjacent the reduction zone is connected by means of a pipe 66 to a vacuum pumping and vent system which permits (a) pumpdown of the system to remove all air, and (b) venting of the system when its pressure rise is excessive. In a preferred embodiment, the vent pipe 66 is connected to a manifold 63, one arm of which leads to a shell and tube condenser 70 positioned in a furnace schematically indicated at 72. The condenser tubes are indicated at 74 and are shown as being eccentrically mounted with respect to the shell so as to provide a larger space adjacent the entrance to the condenser than adjacent the exit thereof. The ternerature of tubes 74 is controlled by operation of a vacuum pump 76 which normally maintains tubes 74 under a vacuum and can draw either cold air or hot air through the tubes 74 by manipulating valves 78 and 3t) respectively. The manifold 63 also preferably includes a safety valve 82 for venting the whole system to a stack in the event of a sudden pressure rise. By means of a vacuum pumping system 34, the gases from the reduction zone 22 are drawn through the condenser or are drawn directly from the zone, by-passing the condenser by opening a valve 83 provided in a direct line from the manifold 68 to the vacuum pumping system 84 and closing a valve '75 provided in the line from the condenser 79. It is prcferred to by-pass the condenser during the initial pumpdown for improved pumping efficiency. During the reaction it is preferable to maintain the venting system under vacuum as shown to obviate the possibility of back-leakage of air into the reduction zone. This pumping system 8% preferably includes steam ejectors and a barometric condenser which serves the additional function of a scrubber for removing noxious gases.

In a preferred method of operating the apparatus described above, a tub 26 containing a charge 28 of clean magnesium ingots is placed in the end of the retort 20. The baffle 38 is next placed in the retort followed by the several containers 30 of pure zirconium tetrachloride, The pipes 62 and 64 are then connected to the baffle 38 and the plug 44 respectively, and the plug is inserted in position. The outer door 54 is then closed and the retort is evacuated by means of vacuum pumping system 84. During this initial pumpdown, it is preferred that the vent condenser 70 be by-passed by opening valve 33 and closing valve 75. The whole retort and condenser system is gradually heated to a few hundred degrees centigrade, while evacuated, to drive off volatile impurities such as adsorbed water vapor and air on the inner surfaces of the retort and to decompose any water-bearing materials in the zirconium tetrachloride. Other volatile impurities such as aluminum chloride and the like are also driven from the retort and the reactant charged during this initial heat-up. If desired, during this stage, a partial pressure of hydrogen may be introduced into the reactor to reduce ferric chloride to ferrous chloride. During this period of operation at low pressure, the interior of baffle 38 and plug 44 are maintained at subatmospheric pressure also to prevent damage to these elements. When all of the impurities have been driven from the interior of the retort, the bypass valve 83 is closed and the interior of the retort 20' is brought up to a pressure slightly in excess of atmospheric pressure by introducing argon through the pipes 43. At-the same time the plug 44 and the barrier 38 are also pressurized with argon. The reduction zone is then brought up to a temperature of above 850 C. and heating of the'volatilization zone 24 is commenced.

As the zirconium tetrachloride is volatilized, it passes upwardly through the micrometallic filters 33, through the opening 40in thetop of the baffle 38, along the conduit 42 and down onto the surface of the molten magnesium 28. The zirconium tetrachloride vapors react with the molten magnesium to form zirconium metal and magnesium chloride. If the temperature in the reduction zone 22 should start to rise, indicating too rapid a reaction, cold air is sucked through the control condenser pipes 50, the pressure of air in these pipes being always maintained at less than the pressure inside of the retort 20. The cooling of the condenser pipes 50 will cause condensation of zirconium tetrachloride'vapors on these pipes so as to reduce the partial pressure of. zirconium tetrachloride in the volatilization zone. At the'same time blowers 19 can be operated to cool off the furnace, this being achieved at both ends of the furnace or only adjacent the volatilization zone 24. If the control condenser is not completely effective to slow down the reaction, several additional control steps can be taken. An additional partial pressure of argon can also be introduced through the pipe 43 to effectively reduce the partial pressure of zirconium tetrachloride in the reactor. Also the system can be vented through the vent condenser 70 by opening valve 75 while the tubes 74 are being cooled by sucking cold air at subatmospheric pressure through these tubes. When the reaction temperature has thus been brought under control by slowing down the reaction, valve 75 is closed and the condensed zirconium-tetrachloride on the tubes 74 can be revaporized into the system by sucking hot furnace air through the tubes 74. Since all of the other portions of the manifold are at an elevated temperature, the only two places where the zirconium tetrachloride vapors have condensed during this control operation are the vent condenser tubes 74 and the control condenser tubes 50 carried by plug 44. When the flow of cold air through these condenser tubes 50 is stopped, the zirconium tetrachloride condensed thereon will revaporize due to the fact that the interior of the volatilization zone 24 is maintained above the sublimation temperature of zirconium tetrachloride.

1 As will be apparent from the above discussion of the invention, the amount of zirconium tetrachloride vapors available for reaction can be readily controlled in most cases by:

(a) Maintaining furnace 14 at a desired temperature and (b) Temporarily removing excess zirconium tetrachloride vapors by condensing them on control condenser 50.

When additional controls are needed, they can be provided by:

(a) The use of vent condenser 70,

(b) Flooding the reactor with argon through pipe 43, and

(c) Cooling the reactor zone and vaporization zones by means of the blowers 19.

In the event that, despite these controls, the reaction gets out of hand and an .excess pressure is generated in the retort, the whole system is vented through safety valve 82 to a stack thereby preventing damage to the retort.

When the reduction reaction has been completed, the heaters 18 are turned ofl and the furnace retort is cooled by means of blowers 19. When it has been brought down to the ambient temperature, it is opened up and the various elements are removed by lift trucks or similar equipment.

While the invention is described primarily in connection with the production of zirconium, it is obviously equally applicable to the production of other metals wherein a normally solid halide is vaporized and fed into a reaction zone where it is reacted with a molten reducing agent to form the desired metal.

Since certain changes may be made in the above apparatus without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. An apparatus for reducing vaporizable refractory metal compounds with a metallic reducing agent comprising a furnace chamber, a horizontally disposed retort having top, bottom, side and end walls mounted in said furnace chamber, an upwardly extending heat insulating 8 partition mounted in said retort and dividing the space therein into horizontally spaced vaporizing and reaction zones, said partition wall having an opening therein adjacent the top wall of said retort, means for supporting a vaporizable solid refractory metal compound in said vaporizing zone at a point therein below said opening in said partition wall and means for supporting said metallic reducing agent in said reaction zone at a point below said opening in said partition Wall, said opening in said partition Wall providing a horizontally extending path of flow for vapors from said vaporizing zone to said reaction zone at a point above that in said vaporizing zone at which said metal compound is vaporized and above a point in said reaction zone at which said metallic reducing agent is disposed.

2. The apparatus of claim 1 wherein said partition wall is a heat insulated wall adapted to maintain said reaction zone and said vaporizing zone at different temperatures.

References Cited in the file of this patent UNITED STATES PATENTS 1,576,083 Boyer Mar. 9, 1926 2,556,763 Maddex June 12, 1951 2,773,760 Winter Dec. 11, 1956 2,827,371 Quin Mar. 18, 1958 2,828,199 Findlay Mar. 25, 1958 2,843,477 Booge July 15, 1958 FOREIGN PATENTS 628,147 Great Britain Aug. 23, 1949 995,904 France Aug. 22, 1951 489,090 Canada Dec. 23, 1952 

1. IN AN APPARATUS FOR REDUCING VAPORIZABLE REFRACTORY METAL COMPOUNDS WITH A METALLIC REDUCING AGENT COMPRISING A FURNACE CHAMBER, A HORIZONTALLY DISPOSED RETORT HAVING TOP, BOTTOM, SIDE AND END WALLS MOUNTED IN SAID FURNACE CHAMBER, AN UPWARDLY EXTENDING HEAT INSULATING PARTITION MOUNTED IN SAID RETORT AND DIVIDING THE SPACE THEREIN INTO HORIZONTALLY SPACED VAPORIZING AND REACTION ZONES, SAID PARTITION WALL HAVING AN OPENING THEREIN ADJACENT THE TOP WALL OF SAID RETORT, MEANS FOR SUPPORTING A VAPORIZABLE SOLID REFRACTORY METAL COMPOUND IN SAID VAPORIZING ZONE AT A POINT THEREIN BELOW SAID OPENING IN SAID PARTITION WALL AND MEANS FOR SUPPORTING SAID METALLIC REDUCING AGENT IN SAID REACTION ZONE AT A POINT BELOW SAID OPENING IN SAID PARTITION WALL, SAID OPENING IN SAID PARTITION WALL PROVIDING A HORIZONTALLY EXTENDING PATH OF FLOW FOR VAPORS FROM SAID VAPORIZING ZONE TO SAID REACTION ZONE AT A POINT ABOVE THAT IN SAID VAPORIZING ZONE AT WHICH SAID METAL COMPOUND IS VAPORIZED AND 